Strong, high purity nickel

ABSTRACT

A nickel powder metallurgy product containing very small amounts of carbon, oxygen, magnesium, and aluminum is characterized by very high strength and fine grain.

United States Patent [191 Morse STRONG, HIGH PURITY NICKEL [75IInventor: Jeremy Painter Morse, Chesapeake,

Ohio

[73] Assignee: The International Nickel Company.

Inc.. New Yorkv NY.

{22] Filed: Mar. [6, 1973 [2|] App]. No: 342,034

Related U.S. Application Data [63] Continuation-in-part of Ser. No.[57.004. June 25.

l9? l, abandoned.

[ July 22, 1975 Weizenbach et al. 75/206 Tracey et al 75/206 OTHERPUBLICATIONS Rosenberg. Nickel and Its Alloys. NBS Monograph I06, U.S.Dept. of Comm. May I968, p. 48.

Primary Exuminer-Leland A. Sebastian Assistant Examiner-B. H. HuntAllurney. Agent, or Firm-M, W. Leff; E. C. MacQueen [57] ABSTRACT Anickel powder metallurgy product containing very small amounts ofcarbon, oxygen. magnesium. and aluminum is characterized by very highstrength and fine grain.

14 Claims, N0 Drawings 1 STRONG, HIGH PURITY NICKEL This application isa continuationin-part of US. application Ser. No. l57.004. filed June25. l97l now abandoned.

The present invention relates to a method for producing dispersionstrengthened nickel by powder metallurgy and to the product resultingtherefrom.

Wrought commercially pure nickel is desirable in many applications dueto the high toughness. ductility. corrosion resistance and weldabilityof nickel. Thus. typical applications include food processing equipment.chemical handling equipment, electrical and electronic parts. aerospaceand missile components, caustic handling equipment and piping. rocketmotor cases. transducers. etc. Nickel compositions of high purity arecharacterized by shortcomings including. for example in the case of flatproducts such as sheet or strip. the formation of Luders lines or bands.which are surface irregularities attributable to localized yielding uponflexing. Also. nickel compositions are susceptible to undesirable graingrowth upon heating to high temperatures. and for many applications. areregarded as having insufficient strength.

Conventional nickel products of high purity can be produced by meltingand casting or can be produced by power metallurgy. Nickel products areamenable to production by powder metallurgy since carbonyl nickel powderof high purity is readily available. Some of the shortcomings ofcommercially available high purity nickel products could apparently besolved by. for example. alloying magnesium in small amounts in nickel soas to increase the strength and refine the grain of the resultingproduct. However. it is found that magnesium in excess of0. l percentproduces detrimental porosity in welds. lnclusion of a fine dispersoidsuch as alumina in nickel produced by the powder metallurgy would alsoseem to provide a means for increasing the strength and for refining thegrain ofthe product. However. it is found that inclusion of an amount ofline alu mina on the order of about one volume per cent in nickelproduced by powder metallurgy still results in room temperature and hightemperature tensile strengths which are insufficient. Furthermore, evenas low an amount as volume per cent of alumina dispersed in nickel isfound to impair high temperature ductility. In fact. even as little as avolume per cent of alumina in nickel impairs vveldability due toporosity. Accordingly, the potential strengthening effect of alumina innickel produced by powder metallurgy cannot. as a practical matter. berealized.

It is an object of the present invention to provide. by powdermetallurgy. a nickel product of high purity characterized by improvedstrength at room temperature and at elevated temperatures. by resistanceto grain coarsening upon heating to high temperatures, and which isweld-able.

A further object of the invention is to provide a high purity nickelproduct which in the form of sheet or strip does not exhibit Luderslines or bands.

Generally speaking. the process to which the present invention isdirected comprises mixing a highly pure. fine nickel powder. eg. ahighly pure carbonyl nickel having an average particle size of about 7microns or less. about 0.0l percent to about 0.06 percent by weightoffine alumina powder having a particle size not exceeding about 0.10microns. e.g.. about 0.01 to about 0.03 microns. about 0.07 percent toabout 0.] percent fine magnesium powder. up to about 0.15 percent or0.20 percent carbon. compacting the mixture. cg. hydrostatic pressing.sintering the compact in a protective atmosphere such as dry hydrogen ata temperature in excess of the boiling point of magnesium. andpreferably at a temperature of at least 1 175C. and then hot working theresulting sintered product by conventional means. As an alternative. thepressing opera tion may be eliminated. In this method. the blendedmixture is poured into a mold coated so as to prevent sticking of thepowders at high temperatures. The mold is then secured by sand sealagainst the ingress of combastion gases from the sintering furnace. Thesintering atmosphere. e.g.. dry hydrogen. is admitted to the mold via agas inlet pipe. and escapes through the sand seal of the mold. The moldassembly is then placed in the sintering furnace. and sintering proceedsas described below.

Carbonyl nickel powder being an average particle size of about 4 to 7microns is satisfactory for use in the process. Fine alumina having aparticle size of about 0.03 microns is also satisfactory. Desirably thecarbon is introduced into the mixture as a fine powder. e.g.. minus 325mesh. preferably carbon powder coated with nickel as. for example. bythe carbonyl technique.

Magnesium must be included in a form such that it can reduce thealumina. Preferably. the magnesium is introduced elemental magnesiumpowder. Possibly a powdered alloy of magnesium can be used; however. thereaction rate will be slower. and higher temperatures may be required tovaporize the magnesium.

The blended mixture may be compacted at pressures up to. for example.about 30.000 pounds per square inch so as to form a selfsustainingcompact or billet having a theoretical density of at least percent.e.g.. an apparent density of about 5.8 gm/cc. The billet may then besintered in flowing hydrogen. cracked ammo nia. or other reducingatmosphere containing at least 10 percent. and preferably at least 30percent hydrogen having a dew point not higher than minus 60F.

in the consolidated product resulting from the aforementioned processingprocedure. it appears that the refractory oxide content thereof ispresent in finer particulate form than that of the initial aluminaintroduced into the mix. On the basis of presently available analyticaltechniques. it appears that alumina is converted to aluminum andmagnesium is converted to magnesia.

In a preferred embodiment ofthis invention. the rela tive levels ofmagnesium and alumina used in preparing the alloys are such that atleast sufficient magnesium is present. stoichiometrically. to reduce allof the alumina present to metallic aluminum. it appears that in suchembodiment. substantially no alumina in particulate form is present inthe nickel product; instead. available techniques indicate that the bulkofthe aluminum lie. greater than percent added initially as alumina powder is present in the nickel product as aluminum metal dissolved in thenickel matrix. When sufficient magnesium is employed in the initialmixture a portion thereof appears. by the best techniques available. tobe present as magnesium metal dissolved in the nickel matrix. while aportion thereof appears to be present as finely divided magnesia. andthat such magnesia dispersoid has a particle size of less than about 0.lmicron.

Satisfactory products in accordance with the inven tion contain up toabout 0.20 percent carbon. about 0.004 percent to about 0.04 percentaluminum. about 0.7 percent to about 0. percent magnesium. with thebalance apart from oxygen essentially nickel. Trace impurities may. ofcourse. be present. Oxygen in the product is present substantially inthe form of magnesia. The concentration of the magnesia dispersoid isabout 0.1 percent to about 0.25 percent by volume. 1t can be pointed outthat the amount of magnesium present as metal can be determined byheating a thin sheet or strip about 0.005 inch thick in an oxidizingatmosphere comprising hydrogen saturated at room temperature with watervapor to a temperature of about 1092C. for hours so as to causemigration of metallic magnesium to the surface of the metal bydiffusion. where it becomes oxidized. Such magnesium oxide can beremoved by pickling and when the metal of the remaining body is analyzedfor magnesium this magnesium can be taken as that present in the oxideform, since such magnesium cannot diffuse. Generally. about to aboutpercent. e.g.. about 50 percent, of the magnesium will be present inmetallic form In one embodiment of this invention the alloy containsabout 0.10 to about 0.20 percent carbon. Such alloys. in addition tobeing weldable. are characterized by particularly improved strength atroom temperatures. In another embodiment. the alloys of this inventionare essentially free of carbon. and such alloys. in addition to beingweldable and having improved strength over pure nickel. arecharacterized by having good electrical conductivity.

The sintered mass of billet produced in accordance with the inventioncan be extruded or hot rolled to plate. bar or tube shell and can beconverted to the usual mill forms such as plate. sheet. strip. rod,wire, tubing. etc. Because of the relatively high sintering temperature.sintered billets produced in accordance with the invention will have anapparent density of at least about percent.

For the purpose of giving those skilled in the art a betterunderstanding of the invention. the following illustrative examples aregiven:

EXAMPLE 1 A 10 kg. mixture consisting essentially of. by weight. about0.08 percent elemental magnesium powder (minus 325 mesh); 0.012 percentalumina powder having an average particle size of 0.03 microns; 0.16percent carbon in the form of minus 325 mesh nickelcoated carbon powderparticles containing 25 percent carbon; and the balance 4 to 7 micronparticle size carbonyl nickel powder having carbon. iron. and oxygencontents of about. respectively. 0.054. 0.003. and 0.062 percent. wasmechanically blended in an 8 quart capacity twin shell blender for aperiod of about 20 minutes. Thereafter. the blended powder charge washydrostatically pressed at 30.000 psi into a billet approximately 4 inchdiameter and 9 inches long. The billet was sintered in hydrogen at about1200C. for about 8 hours. Half of the sintered billet was hot finished.hot-forgcd at about 1 175C.. from a 4 inch diameter to a /4 inch squarebar. which bar was then reheated to 1 175C. and forged to a inchdiameter rod.

The remaining half of the 4 inch diameter billet was hot forged to ainch thick by 2 inch strip. which was subsequently heated and hot-rolledat about 1 175C. to 0.187 inch thick strip. This strip was annealed at980C. for one hour and cold rolled to 0.056 inch thick strip. Both theinch diameter rod and the 0.056 inch thick strip were annealed.respectively, at 980C. for /2 hour and 1025C. for 3 minutes and testedwith the results set forth in the following Tables 1 through V.

TABLE 1 Tensile Strength Yield Strength Elon ation Reduction Alloy (ksi)(0.2% offset) ksi of Area TABLE 11 Cold-Rolled Annealed Strip RoomTemperature Properties Tensile Strength Yield Strength Elon ationReduction Alloy (ksi) (0.2% offset) ksi & of Area cold-rolled subsequentto but working TABLE III GRAIN SIZE OF STRIP VERSUS ANNEALING CONDITlONAnneal 1023C./3 1150C./3 1 C./1 1023C./3 l023C./3 ing min. min. hr. min.min. Con: 1 150C./1 1 150C./24

ditlon hr. hrs.

Alloy 1 No. 8.5 No. 8.5 No. 8.5 No. 8.5 No. 8.5

Alloy A No. 6.5 No. 3 No. 0 No. 000

all material coldworked at least 50% prior to annealing and grain sizegiven in ASTM number equivalents.

TABLE IV HOT FINISHED ANNEALED ROD I200F. PROPERTIES cold-rolledsubsequent to hot working The results of the room temperature testsperformed on the above-mentioned annealed rod and annealed strip of thedispersion-strengthcned nickel alloy. designated as Alloy l. arecompared in Tables I and II with nominal values for commercial wroughtnickel alloy rod and sheet in an annealed condition. containing, byweight. 0.08 percent carbon. 0.18 percent manganese, 0.2 percent iron.0. l 8 percent silicon and designated as Alloy A in the Tables. Datagiven are for material produced by melting and casting. Tis comparisonindicates the dispcrsionstrengthened nickel alloy (Alloy l )to besuperior to the wrought nickel (Alloy A). Specifically. the roomtemperature tensile and yield strengths of the sheet and rod of thepresent invention are at least percent higher than those for Alloy A.and the elongation characteristics of both compositions are generallycomparable.

From the measured grain sizes (Table III) of respective strips of AlloyA and the measured grain size of Alloy l of the present invention. allafter cold working at least 50 percent and the various annealingtreatments shown in Table III. it can be seen that the wrought nickelproduct (Alloy A) exhibits significant grain growth with increasingannealing time and/or annealing temperature. whereas the grain size ofthe strip provided in accordance with the present invention appears toremain constant over the range of annealing conditions investigated.This factor, and the fine grain size found. is of advantage in providingflat sheet for deep drawing and other applications. The high temperaturetest results (Tables IV and V) for the abovementioned bars and stripsprovided in accordance with the invention (Alloy l and the nominal hightemperature values for wrought nickel bars and strips (Alloy A) showthat, for annealed condition. the powder metallurgy product of theinvention provides significant improvements in tensile strength andyield strength over the commercial wrought nickel products at bothl200F. and 1600F.. the yield strength of the present product being abouttwo to three times as great as that for the wrought nickel product, andthe elongation being retained substantially at the higher temperatures.The sintered product contains 0.14 percent carbon. 008 percentmagnesium. 0.006 percent aluminum. and the balance, apart from oxygen,nickel. Activity data kit shows that roughly 50 percent of the magnesiumremains as elemental magnesium in the product.

EXAMPLE II A second mixture having the same constituents and correlatedproportions as the l0 kg. mixture above and weighing about l637 kg. wasmechanically blended in a 20 cubic foot capacity twin shell blender forone hour. after which all of the blended powder was hydrostaticallypressed to a billet about l2 inches in diameter and I20 inches long. Thebillet was sintered in hydrogen at 1200C. for 9 hours. The sinteredbillet was then hot rolled at about ll50C. to a slab about 7 inchesthick and about 13.5 inches wide. The slab was reheated to 1 C. and hotrolled to a hot band A inch thick and 29 inches wide. The hot band wasannealed at about 980C. for about 6 minutes at temperature, pickled innitric acid-hydrofluoric acid solution. and cold rolled to a 0.110 inchthick strip. The 0.] 10 inch thick strip was belt ground and thencold-rolled further to produce a 0.056 inch thick strip. The strip wasthen continuously bright annealed at 980F. for 3 minutes in a hydrogenatmosphere. The analysis of the sintered product of Example ll wassubstantially the same as that reported under Example I.

There was no visible evidence of Luders banding on the surface of thecold worked and annealed strip of the present invention that wasproduced in accordance with the procedure described in the Examples.Strip produced in accordance with the Examples was welded readily by theTIG process to produce sound. crackfree welds.

EXAMPLE lll Two 10 kg. mixtures were prepared. One consisted essentiallyof. by weight, about 0.08 percent elemental magnesium powder (-325mesh); 0.012 percent alumina powder having an average particle sizeof0.03 microns. 0.16 percent carbon in the form of 325 meshnickel-coated carbon powder particles containing 25 percent carbon. andthe balance 4 to 7 micron particle size carbonyl nickel powder havingcarbon, iron and oxygen content of about. respectively. 0054 percent.0.003 percent, and 0.062 percent. The second mixture was identical inall respects except that no carbon powder was added. Both of themixtures were mechanically blended in an 8-quart capacity twin-shellblender for a period of about 20 minutes, and subsequently pressed,

TABLE VIII GRAIN SIZE OF STRIP* ANNEALED l(l23C'./3 min.

. Alloy ASTM GRAIN SIZE sintered, hot worked and annealed in a manneridenti- 5 cal to that described in Example I. The powder containingcarbon is similar to the alloy prepared in Example I. and is referred toherein as Alloy la. The second al- A as loy, which is essentiallycarbon-free, is referred to as AIIOy U "All material cold \uirkcil atleast 5074 prior to annealing.

In the following Tables VI to XI, the properties of "miwlvdm TABLE IXHOT FINISHED AND ANNEALED ROD I200F. PROPERTIES Alloy Tensile StrengthYield Strength Elongjition Reduction (ksi) (0.2% oflset) ksi of Area la29.3 16.3 3L0 37.0 2 24.6 l0.l 44.0 4L9 I600F. PROPERTIES la 10.6 8.1 3833.2 2 E08 83 24 20.3

TABLE X COLD ROLLED. ANNEALED STRIP I200F. PROPERTIES Tensile StrengthYield Strength Elongation Reduction Alloy (kSl) (0.2% offset) ksi ofArea 7c la 26.3 I l.6 39.5 2 23.4 8.9 41.5

these two compositions are compared with nominal TABLE XI values foreither commercial products, viz. a commerc'- l wro h n' kel d t nd or ac mmercial ure ug I pro m O p ROOM TEMPERATURE nickel product. Alloy A.as described In Example I, re- ELECTRICAL RESSTWITY, fers to acommercial wrought nickel alloy rod and sheet Alla;v Resistivity in anannealed condition, containing, by weight, 0.08 It cml percent carbon,0.l8 percent manganese, 0.2 percent u ml iron, 0. l8 percent silicon.Pure nickel is a highly pure 2 7.3 commercial nickel having a nominalnickel content of A Pure Nickel 7.48 99.97 percent and containingtypically less than about 0.02 percent, by weight. carbon. Reliabilityol'uilucs is :w

TABLE VI HOT-FINISHED AND ANNEALED ROD Room Temperature PropertiesTensile Strength Yield Strength Elongation Reduction Alloy (ksi) (0.2%ofl'set) ksi of Area la 79.2 25.5 65.6 2 57.l 2L3 83.9 Pure Ni 50 I6 50Pure Nickel properties for Hot finished samples which have not beenannealed TABLE VII COLD ROLLED. ANNEALED STRIP ROOM TEMPERATUREPROPERTIES Alloy Tensile Strength Yield Strength Elongation (ksil lllZCloffset) ksi i4 la 83.2 27.8 44.5 I 60.2 l7.h 44.7 Pure Ni 50 lo 50 Withregard to the grain size. it will be noted that the pure nickelrecrystallizes at a lower temperature than the alloys and was thereforeannealed at a lower temperature. However. even at the lower annealingtemperature. the pure nickel has a coarser grain size. With regard tothe properties at higher temperatures. it is believed that similaradvantages in strength at elevated temperatures are present in thealloys of this invention with respect to pure nickel.

Analyses of Alloys la and 2 show: Alloy lucontains 0.13 carbon, 0.076percent magnesium, and 0.007 percent aluminum. Alloy 2 contains lessthan 0.0] percent carbon 0.073 percent magnesium, and 0.007 percentaluminum. The balance in each alloy. apart from oxygen. is essentiallynickel. The magnesium activity of Alloy la is 60.5 percent and that ofAlloy 2 is 64.5 percent.

EXAMPLE IV In an alloy of this invention prepared as described inExample I (Alloy l various analytical procedures were followed todetermine the nature of the dispersoid. it was determined by X-rayresidue analysis from a 10 percent bromine in methanol solution that thesample was free of A1 and it was determined by X-ray residue analysisfrom a percent phosphoric acid in water solution that nickel oxide wasnot present. The alloy was also analyzed by electron microscopy andelectron diffraction. From these analytical procedures the dispersoidwas identified as magnesium oxide. [t is believed. upon study of theresults. that the alloy is dispersed with two types of magnesium oxide.One type is round. uniformly distributed. and about 0.0l micron. Thesecond type is in the form of rather large crystallites of MgO. randomlydistributed. Scanning electron microscopic examination of the dispersoidstrengthened products at a definition of about 5 microns indicates thatmagnesium-rich areas are distributed throughout the product. Thetechnique applied also demonstrated that no coalescence of dispersoidparticles had taken place as a result of processing in accordance withthe invention. Further evidence indicating extremely fine subdivision ofthe dispersoid particles in the final nickel products is taken from thefact that high strength properties are obtained in accordance with theinvention. particularly in view of the small amounts of alloyingmaterial included in the nickel product. Additionally. themicrostructure of the nickel product is remarkably clean when viewedoptically at magnifications up to 200 diameters.

EXAMPLE V Samples of Alloys la and 2 of Example III were analyzedfurther to determine the nature of the dispersoid and the extent ofconversion of alumina and magnesium charged to the initial mixture. Theresults given below were obtained using Atomic AbsorptionSpectrophotometry since it is believed to be the most accurate techniqueavailable for this purpose. The analytical procedure used involvesseparation of the product into two components. the first being asolution which will contain elemental Mg. MgO. and elemental Al. and thesecond a residue which will contain aluminum other than elemental Al(e.g. ALO and MgAl O and any magnesium other than that present aselemental Mg and MgO (e.g.. MgAl O With respect to the aluminum content,it was determined by the above procedure that about 0.000! percent ofAlloy la and about 0.0002 percent of Alloy 2 remains as an oxide. e.g.,as A1 0 or MgAl O That is. in Alloy 2 roughly 97 percent of the aluminuminitially charged as M 0 is converted to elemental aluminum.Accordingly. only about 3 percent of the aluminum added as Al O in theoriginal blend remains as oxide in the final product.

With respect to magnesium. activity determinations showed that more than50 percent of the initial magnesium is converted to oxide. Furtheranalysis by the Atomic Absorption spectrophotometry procedure describedabove shows that only about 0.0002 percent of Alloy la and 0.0003percent of Alloy 2 is present in a form other than elemental Mg or MgO.(Possibly it is present as MgAl O In Alloy 2 this represents less than Ipercent of the total magnesium oxide. Accordingly, 99 percent of theoxidized magnesium appears in the form of MgO.

Thus, substantially all of the initial A1 0 i.e., over percent in thesealloys, is converted to elemental Al. and the dispersoid is essentiallyin the form of MgO.

Although the invention has been explained in terms of initial nickelpowder mixtures containing added carbon. alumina, and magnesium, othercombination of ingredients may be employed to produce the same effect.Thus. oxygen may be introduced as a refractory oxide such as TiO inplace of alumina. provided the requirement is met that the free energyof formation of the oxide of the reducing metal in the sinteringtemperature range is higher than the free energy of formation of theadded refractory material in the sintering temperature range. togetherwith the further requirement that the added reducing metal be in thevapor state at the high sintering temperature employed. It should alsobe noted that in the embodiment of this invention discussed above, inwhich magnesium is the reducing agent, other sources of oxygen may beused other than alumina, provided, as indicated above. the oxides arestable up to the temperature at which the magnesium vaporizes andprovided that the free energy of formation of magnesia is greater thanthat of the additive oxide. Thus. it is possible to use an oxide, forexample, of nickel. cobalt. iron, copper, manganese. and tungsten in theplace of the alumina. Sufficient oxide should be present to oxidizeabout 10 percent of the magnesium. It is believed that the principalfunction of the alumina in the mixture is that it serves as a source ofoxygen which source is intimately mixed with and dispersed throughoutthe initial mixture. The alumina is particularly advantageous because itsatisfies the technical requirements, it is readily available in thedesired fine particle size, and it is relatively inexpensive.

While the reaction which occurs during the sintering of powder mixturesas contemplated in accordance with the invention is not fullyunderstood. it has been found essential that the sintering be conductedat a temperature exceeding substantially the boiling point of magnesium.and preferably at a sintering temperature of at least 1 C. It isbelieved that the magnesium metal content of the nickel powder mixtureevaporates at the high sintering temperature and permeates theinterstices between the solid nickel particles which form the sinteringenvironment. In this way, opportunity is afforded for magnesium vapor toreduce the alumina particles, so as to convert the alumina to alumil I ll num metal with the production of magnesia. it is to be recognized thatoxygen in small amounts may be available in the sintering environment.as from the nickel powder. the atmosphere, etc. and this oxygen cancombine as magnesia. It is to be borne in mind in this connection thatthe free energy of formation of magnesia in the sintering temperaturerange (e.g. 1 175C. to about l400C.) is higher than is the free energyof formation of alumina in this temperature range. The fore goingexplanation seems to fit the experimental data insofar as they can beascertained. Whatever the mechanism. it is found that where sufficientmagnesium is present to reduce the alumina, the final consolidatednickel product is substantially free of alumina, per se. i.e. itcontains less than about 10 percent and preferably less than aboutpercent of A1 0 Available analytical techniques demonstrate that thealuminum present in the final consolidated product is presentessentially as the metal and not as an oxide. and also that 50 percentor more of the magnesium is converted substantially to MgO.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention. as those skilled in the art will readily understandv Such modifications and variations are considered to be withinthe purview and scope of the invention and appended claimsv What isclaimed is:

l. A method of producing a dispersion-strengthened nickel alloy powdermetallurgy product comprising:

a. providing a blended powder charge consisting essentially of, byweight, up to about 0.2 percent carbon. about 0.07 to about 0.] percentmagnesium;

a metal oxide as a source of oxygen, said metal oxide being present insufficient amount to oxidize at least percent of the magnesium tomagnesia, said metal oxide being stable at the temperature at which themagnesium vaporizes, and said metal oxide having a free energy offormation less than that of the magnesia; and the balance fine nickelpowder;

b. sintering the powder mixture in a reducing atmosphere at atemperature at least in excess of the boiling point of magnesium in saidcharge to convert metal in said metal oxide to the elemental state andmagnesium to magnesia and to form a sintered billet; and

c. thereafter hot working the sintered billet to provide adispersion-strengthened product.

2. A method of producing a dispersion-strengthened nickel alloy powdermetallurgy product comprising:

a. providing a blended powder charge consisting essentially of, byweight. up to about 02 percent carbon, about 0.01 to about 0.06 percentaluminum oxide, about 0.07 to about 0.1 percent of magnesium, and thebalance fine nickel powder;

b. sintering the powder mixture in a reducing atmosphere at atemperature at least in excess of the boiling point of magnesium in saidcharge to convert aluminum oxide to aluminum and magnesium to magnesiaand to form a sintered billet; and

c. thereafter hot working the sintered billet to provide adispersion-strengthened product.

3. A method according to claim 2, wherein the powder mixture is sinteredat a temperature of at least about [175C 4. A method according to claim2, wherein said powder mixture is compacted prior to sintering toprovide in the compact a green density of about 5.8 gram per centimeteror more.

5. A method according to claim 2, wherein said sintering is conducted ina hydrogen atmosphere.

6. A method according to claim 2, wherein said nickel powder has anaverage particle size of about 7 microns or less.

7. A method according to claim 6 wherein the fine nickel powder is ahighly pure carbonyl nickel.

8. A method according to claim 2 wherein the magnesium is elementalmagnesium in the form of a fine powder.

9. A method according to claim 2, wherein said alumina powder has aparticle size not exceeding about 0.10 microns.

10. A method according to claim 2, wherein said powder charge consistsessentially of. by weight, about 0.07 to 0. l percent magnesium, about0.01 to 0.06 percent aluminum oxide, and the balance nickel.

11. A method according to claim 2, wherein said powder charge consistsessentially of, by weight. about 0.10 to 0.20 percent carbon, about 0.07to 0. l percent magnesium, about 0.01 to 0.06 percent aluminum ox ide.and the balance nickel.

12. A method according to claim 2, wherein said magnesium in the powdercharge is present in an amount at least sufficient. stoichiometrically,to reduce all of said alumina present to metallic aluminum, wherebyduring said sintering step at least about 90 percent ofthe aluminumoxide is reduced to aluminum, magnesium is converted to magnesia. andabout 40 to percent of the magnesium is retained in metallic form.

13. A method of producing a dispersion-strengthened nickel alloy powdermetallurgy product comprising:

a. providing a blended powder charge consisting es sentially of, byweight. up to about 0.2 percent carbon, about 0.07 percent to about 0.lpercent magnesium, a metal oxide as a source of oxygen, said metal oxidebeing a member of the group consisting of an oxide of Al, Ti, Ni. Co.Fe, Cu, Mn, and W, and said metal oxide being present in sufficientamount to oxidize at least l0 percent of the magnesium to magnesia; andthe balance fine nickel pow der;

b. sintering the powder mixture in a reducing atmosphere at atemperature at least in excess of the boiling point of magnesium in saidcharge to convert metal in said metal oxide to the elemental state andmagnesium to magnesia and to form a sintered billet; and

c. thereafter hot working the sintered billet to provide adispersion-strengthened product.

14. A method according to claim 2, wherein the dis persionstrengthenednickel alloy produced is weldable.

1. A METHOD OF PRODUCING A DISPERSION-STRENGTHENED NICKEL ALLOY POWDERMETALLURGY PRODUCT COMPRISING: A. PROVIDING A BLENDED POWDER CHARGECONSISTING ESSENTIALLY OF, BY WEIGHT, UP TO ABOUT 0.2 PERCENT CARBON,ABOUT 0.07 TO ABOUT 0.1 PERCENT MAGNESIUM, A METAL OXIDE AS A SOURCE OFOXYGEN, SAID METAL OXIDE BEING PRESENT IN SUFFICIENT AMOUNT TO OXIDIZEAT LEAST 10 PERCENT OF THE MAGNESIUM TO MAGNESIA, SAID METAL OXIDE BEINGSTABLE AT THE TEMPERATURE AT WHICH THE MAGNESIUM VAPORIZES, AND SAIDMETAL OXIDE HAVING A FREE ENERGY OF FORMATION LESS THAN THAT OF THEMAGNESIA, AND THE BALANCE FINE NICKEL POWDER, B. SINTERING THE POWDERMIXTURE IN A REDUCING ATMOSPHERE AT A TEMPERATURE AT LEAST IN EXCESS OFTHE BOILING POINT OF MAGNESIUM IN SAID CHARGE TO CONVERT METAL IN SAIDMETAL OXIDE TO THE ELEMENTAL STATE AND MAGNESIUM TO MAGNESIA AND TO FORMA SINTERED BILLET, AND C. THEREAFTER HOT WORKING THE SINTERED BILLET TOPROVIDE A DISPERSION-STRENGTHENED PRODUCT.
 2. A method of producing adispersion-strengthened nickel alloy powder metallurgy productcomprising: a. providing a blended powder charge consisting essentiallyof, by weight, up to about 0.2 percent carbon, about 0.01 to about 0.06percent aluminum oxide, about 0.07 to about 0.1 percent of magnesium,and the balance fine nickel powder; b. sintering the powder mixture in areducing atmosphere at a temperature at least in excess of the boilingpoint of magnesium in said charge to convert aluminum oxide to aluminumand magnesium to magnesia and to form a sintered billet; and c.thereafter hot working the sintered billet to provide adispersion-strengthened product.
 3. A method according to claim 2,wherein the powder mixture is sintered at a temperature of at leastabout 1175*C.
 4. A method according to claim 2, wherein said powdermixture is compacted prior to sintering to provide in the compact agreen density of about 5.8 gram per centimeter or more.
 5. A methodaccording to claim 2, wherein said sintering is conducted in a hydrogenatmosphere.
 6. A method according to claim 2, wherein said nickel powderhas an average particle size of about 7 microns or less.
 7. A methodaccording to claim 6 wherein the fine nickel powder is a highly purecarbonyl nickel.
 8. A method according to claim 2 wherein the magnesiumis elemental magnesium in the form of a fine powder.
 9. A methodaccording to claim 2, wherein said alumina powder has a particle sizenot exceeding about 0.10 microns.
 10. A method according to claim 2,wherein said powder charge consists essentially of, by weight, about0.07 to 0.1 percent magnesium, about 0.01 to 0.06 percent aluminumoxide, and the balance nickel.
 11. A method according to claim 2,wherein said powder charge consists essentially of, by weight, about0.10 to 0.20 percent carbon, about 0.07 to 0.1 percent magnesium, about0.01 to 0.06 percent aluminum oxide, and the balance nickel.
 12. Amethod according to claim 2, wherein said magnesium in the powder chargeis present in an amount at least sufficient, stoichiometrically, toreduce all of said alumina present to metallic aluminum, whereby duringsaid sintering step at least about 90 percent of the aluminum oxide isreduced to aluminum, magnesium is converted to magnesia, and about 40 to70 percent of the magnesium is retained in metallic form.
 13. A methodof producing a dispersion-strengthened nickel alloy powder metallurgyproduct comprising: a. providing a blended powder charge consistingessentially of, by weight, up to about 0.2 percent carbon, about 0.07percent to about 0.1 percent magnesium; a metal oxide as a source ofoxygen, said metal oxide being a member of the group consisting of anoxide of Al, Ti, Ni, Co, Fe, Cu, Mn, and W, and said metal oxide beingpresent in sufficient amount to oxidize at least 10 percent of themagnesium to magnesia; and the balance fine nickel powder; b. sinteringthe powder mixture in a reducing atmosphere at a temperature at least inexcess of the boiling point of magnesium in said charge to convert metalin said metal oxide to the elemental state and magnesium to magnesia andto form a sintered billet; and c. thereafter hot working the sinteredbillet to provide a dispersion-strengthened product.
 14. A methodaccording to claim 2, wherein the dispersion-strengthened nickel alloyproduced is weldable.